Casings for the "Thin Man" plutonium gun weapon, developed during the Manhattan Project. The weapon shape was tested as part of Project Alberta at Wendover Field, Utah. The plutonium gun design was eventually abandoned as un-feasible, as the spontaneous fission rate of reactor-bred plutonium was much higher than expected due to unavoidably high contamination of the Plutonium 239 (²³⁹Pu) with Plutonium 240 (²⁴⁰Pu).

• Immediate source: John Coster-Mullen, Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man (self published, 2005).[1]
• Ultimate source: Los Alamos/Manhattan Project

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